Materials
Everything here was chosen to be buyable in an ordinary Mexican hardware store, aquarium shop or garden centre. No laboratory equipment is required.
Column
| Item | Quantity | Where |
|---|---|---|
| PVC pipe, 3 in | 750 mm | hardware store |
| Volcanic scoria (lava rock), raw | 3 kg | garden centre |
| Fine silica sand, aquarium grade | ~1.3 kg | aquarium or pet shop |
| Lump charcoal, not briquettes | ~0.65 L crushed | any grocery store |
| PVC end cap, 3 in | 1 | hardware store |
| Transparent hose, ½ in | 1 m | hardware store |
| Plastic stopcock, ½ in | 1 | hardware store |
| Plastic insect mesh | 30 × 30 cm | hardware store |
| Two-part epoxy | 1 | hardware store |
The pipe is opaque, so the layers cannot be seen once loaded. Each one is photographed from above as it goes in, which records the build just as well. The silica sand is inert and leaves water chemistry unchanged. Hot-melt glue does not hold on wet PVC; seal the outlet with two-part epoxy.
Measurement
| Item | Quantity | Note |
|---|---|---|
| Identical glass jars | 6 | straight-sided, clear, no embossing |
| Syringes, no needle | 3 × 20 ml | for the dilution series |
| Kitchen measuring jug | 1 L | replaces a graduated cylinder |
| Blue food colouring | 1 | strong, not pale |
| Neutral liquid soap | 1 | surfactant load |
| White card | 80 × 80 mm | exposure reference |
| Printed checker target | 100 × 100 mm | contrast target |
| Constant lamp | 1 | any fixed light source |
The checker target and the white card print together, at true size, on one A4 sheet.
Why the jars must be identical
Every sample is photographed through glass. Different thickness or curvature changes what the camera sees, and the series stops comparing anything. Six matching jam jars work as well as six bought ones.
Blue is not an arbitrary choice. Methylene blue uptake is a useful indicator of the adsorption capacity of activated carbon, so a blue tracer mirrors a real assay — and blue reads as dark grey once the photograph is converted, which is what the contrast measurement needs. Yellow reads almost white and is nearly invisible to the method.
Deliberately not required
| Not needed | Instead |
|---|---|
| Laboratory sieve stack | Insect mesh as a single cut, aperture measured and reported |
| Precision balance | Media placed by depth; volumes recorded rather than masses |
| Geotextile | Discs cut from the same insect mesh |
| Graduated cylinder | Kitchen measuring jug |
| Clamps and stand | Column taped to a mop handle leaning on a wall |
| Nephelometer | Photographs and the analysis code |
Not handled
No perchlorates
Perchlorate salts are strong oxidisers. They are not used, not bought, and not required. Stage 1 is supported by published work; what the bench demonstrates is filtration and adsorption, measured with synthetic greywater mixed to a written recipe.